1. Technical Field
The present invention relates to a constitution of a thrust control valve for controlling the thrust (propulsion) of a secondary propulsion engine, such as a thruster for controlling the orbit and attitude of a flying object, and the speed of the flying object.
2. Description of the Related Art
The attitude of a flying object that flies at high altitudes in the atmosphere cannot satisfactorily be controlled and the orbital control (diversion) of the same cannot satisfactorily achieved only by a control effort generated by a control wing. Therefore, the flying object is provided with a thruster that jets a high-pressure propulsion gas supplied from a chamber containing a propellant. The thruster is provided with a thrust control valve called a propellant valve for controlling the thrust generated by jetting the propulsion gas.
FIGS. 6A and 6B are typical views of a conventional pintle thrust control valve 1 in an open state and in a closed state, respectively. The pintle thrust control valve 1 has nozzle 5 and a plug 9. The nozzle 5 has a gas supply chamber 2 to which a propulsion gas is supplied, a gas jetting chamber 3 the propulsion gas is jetted, and a connecting passage 4 defined by a surface 6 and coaxially connecting the gas supply chamber 2 and the gas jetting chamber 3. The plug 9 is placed for axial movement in the gas supply chamber 2 coaxially with the gas supply chamber 2, the gas jetting chamber 3 and the connecting passage 4. The plug 9 has a taper tip having a taper surface 7. A passage 8 is defined by the surface 6 and the taper surface 7.
The plug 9 is moved axially by a drive system including a motor. The sectional area of the passage 8 is varied according to the position of the plug 9 to control thrust generated by jetting the propulsion gas. The product of the pressure P1 of the propulsion gas in the gas supply chamber 2, and the pressure-receiving area A of the taper surface 7 of the plug 9 is equal to a load F that urges the plug 9 axially away from the surface 6. The load F increases as the required thrust increases, and hence the drive system including the motor for driving the plug 9 is large (EP-A No. 489712).
FIG. 7 is a typical sectional view of another conventional differential thrust control valve 11. The differential thrust control valve 11 has a nozzle 15 and a pair of plugs 19a and 19b. The nozzle 15 has a pair of gas supply chambers 12a and 12b to which a propulsion gas is supplied, a pair of gas jetting chambers 13a and 13b through which the propulsion gas is jetted, and a pair of connecting passages 14a and 14b respectively defined by surfaces 16a and 16b and coaxially connecting the gas supply chambers 12a and 12b, and the gas jetting chamber 13a and 13b, respectively. The plugs 19a and 19b are placed for axial movement in the gas supply chambers 12a and 12b coaxially with the gas supply chambers 12a and 12b, the gas jetting chambers 13a and 13b and the connecting passages 14a and 14b, respectively. The plugs 19a and 19b have taper tips respectively having taper surfaces 17a and 17b. Passages 18a and 18b are defined by the surfaces 16a and 16b and the taper surfaces 17a and 17b, respectively.
The pair of plug 19a and 19b of the differential thrust control valve 11 are moved axially by a motor to change thrusts linearly. Since loads that act on the plugs 19a and 19b cancel each other, the torque to be produced by the motor is smaller than that to be produced by the motor of the conventional pintle thrust control valve 1 shown in FIGS. 6A and 6B. However, opposite thrusts are generated even in a state where any thrust is not necessary and hence the flow rate of the necessary propulsion gas increases (JP11-83396A).
FIGS. 8A and 8B are typical sectional views of a conventional floating-poppet thrust control valve 21 in an open state and in a closed state, respectively. This floating-poppet thrust control valve 21 has a nozzle 25 provided with a gas supply chamber 22 in which a propulsion gas is supplied, a gas jetting chamber 23 through which the propulsion gas is jetted, and a connecting passage 24 defined by a surface 26 and coaxially connecting the gas supply chamber 22 and the gas jetting chamber 23. This thrust control valve 21 also has a plug 29 axially movable in the gas supply chamber 22, the connecting passage 2 and the gas jetting chamber 23 to open and close the connecting passage 24, a poppet 30 fixedly connected to the plug 29 and provided with through holes 33, and a solenoid valve 31 for controlling pressure in a back space 32 behind the poppet 30.
In this thrust control valve 21, the gas supply chamber 22 communicates with the back space 32 by means of the through holes 33 of the poppet 30. The axial position of the plug 29 is changed by adjusting the pressure in the back space by adjusting the opening of the solenoid valve 31.
This floating-poppet thrust control valve 21 is unable to control the generated thrust linearly and hence the solenoid valve 31 is controlled by a pulse width modulation (PWM) drive system. Therefore, a control signal for controlling the solenoid valve 31 acts as noise on a guide signal for guiding the flying object. Thus, it is possible that the control signal reduces the accuracy of guiding the flying object (JP2000-283301A).